For use as recording media in disk recording-playback devices, magneto-optical disks have been developed which permit rewriting and have a great memory capacity and high reliability. Such disks have found wide use as external memories in computers and audio visual devices.
Developed especially in recent years are techniques for achieving improved recording densities by forming lands 11 and grooves 12 alternately on a signal bearing surface of a magneto-optical disk 1 as shown in FIG. 12 and recording signals on both the lands 11 and the grooves 12. The lands 11 and the grooves 12 are wobbled as illustrated, and the wobbling frequency is a predetermined center frequency as frequency-modulated. A wobble signal is detected by signal reproduction, and the rotation of the magneto-optical disk is so adjusted that the wobble signal has the center frequency at all times, whereby constant linear velocity control is realized. Various items of information (wobble information) such as address information are contained in the wobble signal which is frequency-modulated as stated above. Various control operations are realized based on the wobble information at the time of signal reproduction.
When disk recording-playback devices are in operation for reproducing or recording signals, focus servo or tracking servo is performed for the actuator incorporated in the optical head, based on focus error (FE) signals and tracking error (TE) signals. When the disk recording-playback device is initiated into operation, an offset adjustment is made for focusing or tracking based on the TE signals and RF signals to thereby effect accurate focus servo and tracking servo.
In a process for determining an optimum offset value for a focus error based on the TE signal, as seen in FIG. 19, first, focus offset values are respectively set at at least five different values P0 to P4 centered about an initial value P0, and amplitude values of the TE signal at the respective offset values are measured. Among said at least five points measured, a first point is set at a point having the maximum amplitude value, a second point is set at a point having an offset value smaller than the offset value P0 at the first point and an amplitude value not greater than a value (T0−5) obtained by subtracting a predetermined value from an amplitude value T0 at the first point, a third point is set at a point having an offset value greater than the offset value P0 at the first point and an amplitude value not greater than the value (T0−5) obtained by subtracting the predetermined value from the amplitude value T0 at the first point. With reference to the offset values P0, P1, P4 and the amplitude values T0, T1, T4 at the respective three points, a quadratic curve representing the relationship between the offset values and the amplitude values is determined. An offset value corresponding to the peak of the quadratic curve is determined as an optimum offset value Popt1. A procedure for determining an optimum offset value based on the RF signals is the same as the above.
FIGS. 13 to 15 show a focus offset adjustment procedure to be executed based on the TE signals when the disk recording-playback device is into an initiation operation. First in steps S91 to S94 in FIG. 13, focus offset values are respectively set at an initial value P0, a value P1 smaller than the initial value by eight steps, a value P2 smaller than the initial value by four steps, a value P3 greater than the initial value by four steps, and a value P4 greater than the initial value by eight steps, and amplitude values T0 to T4 are measured at the respective offset values. Among these five points measured, thereafter, a first point is set at a point having the maximum amplitude value. A first offset value Pmax is set at an offset value at the first point. A first amplitude value Tmax is set at an amplitude value at the first point.
Subsequently in step S95, an inquiry is made as to whether a second point having an offset value Px smaller than the first offset value Pmax and an amplitude value Tx smaller than the first amplitude value Tmax by five steps or more is included in four measured points other than the first point. If the inquiry is answered in the affirmative, step S96 follows to set a second offset value PA at the offset value Px at the second point, set a second amplitude value TA at the amplitude value Tx at the second point, and set to “TRUE” a PA—flag indicating whether the second offset value PA is obtained, thereafter followed by step S97.
In step S97, an inquiry is made as to whether a third point having an offset value PX greater than the first offset value Pmax and an amplitude value Tx smaller than the first amplitude value Tmax by five steps or more is included in the four measured points other than the first point. If the inquiry is answered in the affirmative, step S98 follows to set a third offset value PB at the offset value Px at the third point, set a third amplitude value TB at the amplitude value Tx at the third point, and set to “TRUE” a PB—flag indicating whether the third offset value PB is obtained, thereafter followed by step S99 shown in FIG. 14.
When the second point and the third point are both included in the four measured points other than the first point, answers to inquiries in step S99 in FIG. 14 and in step S106 in FIG. 15 are affirmative, followed by step S113. With reference to data on the first to third points (Pmax, Tmax), (PA, TA) and (PB, TB) which are included in the five measured points, the relationship between the offset values and the amplitude values is approximated to a quadratic curve, and an offset value corresponding to the peak of the quadratic curve is calculated as an optimum offset value Popt, to terminate the procedure.
On the other hand, when the second point is not included in the four measured points other than the first point, an answer to the inquiry in step S99 in FIG. 14 is negative. In steps S100 to S105, an offset value P is decreased every four step starting from a value smaller than the initial value P0 by 12 steps, to thereby vary the offset value until when the amplitude value T becomes a value smaller than the first amplitude value Tmax by five steps or more. Then the offset value and amplitude value concerned are respectively set at a second offset value PA and a second amplitude value TA. Accordingly the second point is retrieved. When, in step S113 in FIG. 15, the relationship between the offset values and the amplitude values is approximated to a quadratic curve, the data (PA, TA) at the retrieved second point is used. Incidentally, in retrieving the second point, in the case where the offset value P is smaller than the initial value P0 by 20 steps or more to make the answer to step S101 affirmative, or in the case where the amplitude value T is not greater than a lower limit value TL to make the answer to step S103 affirmative, focus servo deviates to terminate the procedure.
Furthermore, when the third point is not included in the four measured points other than the first point, an answer to the inquiry in step S106 in FIG. 15 is negative. In steps S107 to S112, an offset value P is increased every four step starting from a value greater than the initial value P0 by 12 steps, to thereby vary the offset value until when the amplitude value T becomes a value smaller than the first amplitude value Tmax by five steps or more. Then the offset value and amplitude value concerned are respectively set at a third offset value PB and a third amplitude value TB. Accordingly the third point is retrieved. When, in step S113, the relationship between the offset values and the amplitude values is approximated to a quadratic curve, the data (PB, TB) at the retrieved third point is used. Incidentally, in retrieving the third point, in the case where the offset value P is greater than the initial value P0 by 20 steps or more to make the answer to step S108 affirmative, or in the case where the amplitude value T is not greater than a lower limit value TL to make the answer to step S110 affirmative, focus servo deviates to terminate the procedure.
According to the above procedure, the optimum offset value Popt for the focus error is determined based on the TE signals, and an offset adjustment for focusing is made based on the optimum offset value Popt. According to the same procedure, an optimum offset value for the focus error is determined based on the RF signals, and an offset adjustment for focusing is made based on the optimum offset value. The disk recording-playback device starts signal reproduction or signal recording after the offset adjustment for focusing thus made.
In a usual operation for signal reproduction or signal recording, variations in the ambient temperature, however, lead to the distortion of the housing or parts of the optical head, a shift of position of the optical sensor, variations in the laser wavelength, etc., altering the offset value from an optimum value and consequently impairing the accuracy of focus servo. If the offset value deviates from the optimum value greatly, the bit error rate of reproduced signal exceeds a prescribed value, presenting difficulty in effecting normal reproduction and recording.
In the usual operation, an offset adjustment for focusing is made every time a temperature of the disk varies by a predetermined temperature or more.
In a process of determining an optimum offset value for a focus error based on the TE signals for the usual operation, as seen in FIG. 20, first, focus offset values are respectively set at at least five different values Popt1, P1′ to P4′, centered about the optimum offset value Popt1, i.e., the set value concerned, determined in a previous offset adjustment processing, and amplitude values of the TE signals at the respective offset values are measured. Among said at least five points measured, a first point is set at a point having the maximum amplitude value, a second point is set at a point having an offset value smaller than the offset value Popt1 at the first point and an amplitude value not greater than a value (Topt1−5) obtained by subtracting a predetermined value from an amplitude value Topt1 at the first point, a third point is set at a point having an offset value greater than the offset value Popt1 at the first point and an amplitude value not greater than the value (Topt1−5) obtained by subtracting the predetermined value from the amplitude value Topt1 at the first point. With reference to the offset values Popt1, P1′, P4′ and the amplitude values Topt1, T1′, T4′ at the respective three points, a quadratic curve representing the relationship between the offset values and the amplitude values is determined. An offset value corresponding to the peak of the quadratic curve is determined as an optimum offset value Popt2. A procedure of determining an optimum offset value based on the RF signals is the same as the above.
FIGS. 16 to 18 show a focus offset adjustment procedure to be executed based on the TE signals when temperature variations in excess of or equal to a predetermined value (=5° C.) occur in a usual operation after the system's initiation into operation. First in steps S121 to S124, focus offset values are respectively set at a set value concerned P0′, a value P1′ smaller than the set value by eight steps, a value P2′ smaller than the set value by four steps, a value P3′ greater than the set value by four steps, and a value P4′ greater than the set value by eight steps, and amplitude values T0′ to T4′ are measured at the respective offset values. Among these five points measured, thereafter, the maximum amplitude value is a first point. An offset value at the first point is a first offset value Pmax′. An amplitude value at the first point is a first amplitude value Tmax′.
Subsequently in step S125, an inquiry is made as to whether a second point having an offset value Px′ smaller than the first offset value Pmax′ and an amplitude value Tx′ smaller than the first amplitude value Tmax′ by five steps or more is included in four measured points other than the first point. If the inquiry is answered in the affirmative, step S126 follows to set a second offset value PA at the offset value Px′ at the second point, set a second amplitude value TA at the amplitude value Tx′ at the second point, and set to “TRUE” a PA—flag indicating whether the second offset value PA is obtained, thereafter followed by step S127.
In step S127, an inquiry is made as to whether a third point having an offset value Px′ greater than the first offset value Pmax′ and an amplitude value Tx′ smaller than the first amplitude value Tmax′ by five steps or more is included in the four measured points other than the first point. If the inquiry is answered in the affirmative, step S128 follows to set a third offset value PB at the offset value Px′ at the third point, set a third amplitude value TB at the amplitude value Tx′ at the third point, and set to “TRUE” a PB—flag indicating whether the third offset value PB is obtained, thereafter followed by step S129 shown in FIG. 17.
When the second point and the third point are included in the four measured points other than the first point, answers to inquiries in step S129 in FIG. 17 and in step S136 in FIG. 18 are affirmative, followed by step S143. With reference to data on the first to third points (Pmax′, Tmax′), (PA, TA) and (PB, TB) which are included in the five measured points, the relationship between the offset values and the amplitude values is approximated to a quadratic curve, and an offset value corresponding to the peak of the quadratic curve is calculated as an optimum offset value Popt′, to terminate the procedure.
On the other hand, when the second point is not included in the four measured points other than the first point, a second point is retrieved according to the same procedure as that in an initiation operation as shown in steps S130 to S135 in FIG. 17. When, in step S143 in FIG. 18, the relationship between the offset values and the amplitude values is approximated to a quadratic curve, data (PA, TA) at the retrieved second point is used.
Furthermore, when the third point is not included in the four measured points other than the first point, a third point is retrieved according to the same procedure as that in an initiation operation as shown in steps S137 to S142 in FIG. 18. When, in step S143, the relationship between the offset values and the amplitude values is approximated to a quadratic curve, data (PB, TB) at the retrieved third point is used.
According to the above procedure, the optimum offset value Popt′ for a focus error is determined based on the TE signals, and the focus offset adjustment is made based on the optimum offset value Popt′. According to the same procedure, an optimum offset value for a focus error is determined based on the RF signals, and the focus offset adjustment is made based on the optimum offset value. The disk recording-playback device starts signal reproduction or signal recording after the offset adjustment for focusing thus made. When the disk recording-playback device is in the usual operation, the focus offset adjustment is thus made, consequently effecting focus servo with high accuracy at all times despite variations in temperature of the magneto-optical disk.
However, the disk recording-playback device described has the following problem: in the offset adjustment procedure of the usual operation, the relationship between the offset values and the amplitude values is approximated to a quadratic curve with reference to the previous optimum offset value Popt1, and the second and third offset values P1′, P4′ each having an amplitude value smaller than the amplitude value Topt1 at the offset value Popt1 by a predetermined value or more, as shown in FIG. 20, to increase accuracy of the quadratic curve. For obtaining the second and third offset values P1′, P4′, amplitude values at at least five different offset values Popt1 and P1′ to P4′ need be measured, requiring a long period of time for determining the quadratic curve, thereby entailing the problem of a long period of time taken for the calculation of the optimum offset value.
An object of the present invention is to provide a disk playback device which is adapted to determine the optimum offset value for the error signal in a short period of time when in the usual operation.